Fluorescent whitening agents, I. Bis-4,4'-(4'-methoxy-6'-phenoxy-s-triazin-2'-ylamino)stilbene-2,2'-disulphonic acid : its photodecomposition in solution and on wool.

The collidine salt of bis-4,4'-(4"-methoxy-6"-phenoxy-s-triazin-2?-ylamio)stilbene-2,2'-disulphonic acid (1) has been synthesized from cyanuric chloride. Anhydrous conditions were used so as to avoid contamination by hydrolysis products; the methoxyl groups were radioactively labelled. Irradiation of the trans (E) isomer of (I) in aqueous solution rapidly produced an equilibrium mixture of cis (Z) and trans isomers; decomposition to the corresponding aldehyde (2), acid (3) and dihydro derivative (4) occurred more slowly. Isomerization to the cis form was much slower when (1) was applied to wool and then irradiated; (2), (3) and (4) were also produced and some radioactive material was bound covalently to the wool. No evidence could be obtained for the conversion of (1) into phenanthrene or cyclobutane derivatives or for the occurrence of any photo-Fries rearrangement.